Other Comprehensive Income - Schedule of Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Net (losses) gains arising during the period, Before Tax	$ (7,294)	$ (3,458)	$ 33,329
Less reclassification adjustment for net gains included in net income, Before Tax	(777)	(2,487)	(745)
Net change, Unrealized gains on AFS securities, Before Tax	(8,071)	(5,945)	32,584
Net change in non-credit impairment losses on securities, Before Tax	719	(416)	2,299
Less reclassification adjustment for accretion of credit impairment losses included in net income, Before Tax	(921)	(728)	(661)
Net change, Non-credit impairment losses on securities available for sale and held to maturity, Before Tax	(202)	(1,144)	1,638
Net (losses) gains arising during the period, Before Tax	(4,035)	(12,360)	(20,910)
Less reclassification adjustment for losses included in net income, Before Tax	13,034	7,075	6,663
Net change, Unrealized gains and (losses) on derivatives (cash flow hedges), Before Tax	8,999	(5,285)	(14,247)
Net gains (losses) arising during the period, Before Tax	5,837	6,030	(27,902)
Amortization of prior service cost, Before Tax	(300)	206	305
Amortization of net loss, Before Tax	294	790	226
Net change, Defined benefit pension plan, Before Tax	5,831	7,026	(27,371)
Total other comprehensive income (loss), Before Tax	6,557	(5,348)	(7,396)
Net (losses) gains arising during the period, Tax Effect	3,001	1,458	(13,931)
Less reclassification adjustment for net gains included in net income, Tax Effect	312	1,041	312
Net change in non-credit impairment losses on securities, Tax Effect	3,313	2,499	(13,619)
Net change in non-credit impairment losses on securities	(302)	175	(965)
Less reclassification adjustment for accretion of credit impairment losses included in net income, Tax Effect	382	304	278
Net change, Non-credit impairment losses on securities available for sale and held to maturity, Tax Effect	80	479	(687)
Net (losses) gains arising during the period, Tax Effect	1,574	5,121	8,763
Less reclassification adjustment for losses included in net income, Tax Effect	(5,393)	(2,948)	(2,777)
Net change, Unrealized gains and (losses) on derivatives (cash flow hedges), Tax Effect	(3,819)	2,173	5,986
Net gains (losses) arising during the period, Tax Effect	(2,539)	(2,586)	11,695
Amortization of prior service cost, Tax Effect	119	(89)	(128)
Amortization of net loss, Tax Effect	(109)	(328)	(94)
Net change, Defined benefit pension plan, Tax Effect	(2,529)	(3,003)	11,473
Total other comprehensive income (loss), Tax Effect	(2,955)	2,148	3,153
Net (losses) gains arising during the period, After Tax	(4,293)	(2,000)	19,398
Less reclassification adjustment for net gains included in net income, After Tax	(465)	(1,446)	(433)
Total	(4,758)	(3,446)	18,965
Net change in non-credit impairment losses on securities, After Tax	417	(241)	1,334
Less reclassification adjustment for accretion of credit impairment losses included in net income, After Tax	(539)	(424)	(383)
Total	(122)	(665)	951
Net gains (losses) arising during the period, After Tax	(2,461)	(7,239)	(12,147)
Less reclassification adjustment for losses included in net income, After Tax	7,641	4,127	3,886
Total	5,180	(3,112)	(8,261)
Net gains (losses) arising during the period, After Tax	3,298	3,444	(16,207)
Amortization of prior service cost, After Tax	(181)	117	177
Amortization of net loss, After Tax	185	462	132
Total	3,302	4,023	(15,898)
Total other comprehensive income (loss)	$ 3,602	$ (3,200)	$ (4,243)